1. Field of the Invention
The present invention relates to a calcium phosphate cement which comprises a calcium phosphate powder and a polysaccharide incorporated therein and which, due to this composition, can be hardened easily in a relatively short time using only water not containing an organic acid or the like. The present invention further relates to a calcium phosphate cement composition which comprises a calcium phosphate powder, a polysaccharide, and water, and which can be easily hardened in a relatively short time, especially when an aqueous solution containing the polysaccharide has been used as a liquid for cement mixing.
2. Description of the Related Art
A large number of medical cements of various compositions have previously been proposed for use in living bodies. Calcium phosphate cements for living bodies have an advantage in that this kind of cement upon hardening changes into a bioactive hydroxyapatite, and hence results in a hardened cement having excellent bioaffinity.
Many of the calcium phosphate cements for living bodies comprise tetracalcium phosphate as the main component; see, for example, U.S. Pat. No. 4,612,053, now Reissue Pat. No. 33,161. However, this kind of-cement has a problem in practical use because it requires a relatively long time for hardening. There is also a problem that when a cement paste prepared therefrom is brought into contact with a pseudo body fluid immediately after mixing (i.e., kneading), water penetrates into the paste (i.e., kneaded body) and disintegrates the paste. Consequently, two different methods have been used to apply the cement to a body part where body fluids are present in a large amount. The first method is to apply a cement paste, not immediately after mixing, but instead after it has hardened to some degree. The second method is to apply the cement paste after removal of the body fluids from the body part and after hemostasis, etc. However, these two methods suffer drawbacks in that the cement paste which has hardened to some degree is difficult to handle and has poor workability, and the removal of body fluids, hemostasis, and the like require many hands and much time.
As an expedient for eliminating these problems, a technique for reducing the hardening time using an aqueous solution of either an organic acid (e.g., citric acid or malic acid) or an inorganic acid (e.g., phosphoric acid) as a liquid for cement mixing (i.e., kneading liquid) has been proposed in, for example, JP-A-59-88351 and JP-A-62-83348; the term "JP-A" as used herein means an "unexamined published Japanese patent application". However, when a cement paste prepared with a cement-mixing liquid containing an acid is applied to an inner part of a living body, the paste is highly biostimulative due to the acid, and may cause an inflammatory reaction around the body part to which the paste has been applied. JP-A-2-77261 describes a technique of using an aqueous solution containing chitosan, etc. as a hardener solution so as to inhibit cement disintegration. However, this hardener solution should have a very low pH of approximately 1 to 2, so as to contain the chitosan dissolved therein, and therefore the addition of an acid to the hardener solution is unavoidable. Consequently, this technique also may have the problem of causing an inflammatory reaction, etc. as in the above-described technique.